Aspects of the invention can relate to a light source, a projector, and a method of driving an arc tube.
Related art light source lamps used in light sources for projectors generally have an arc tube and a reflector that reflects the light from the arc tube into a region to be illuminated. It is preferable for this type of light source lamps to make effective use of the light from the arc tube as much as possible.
Accordingly, as a technique for making the best use of the light from the arc tube, a light source lamp can be provided that further includes an auxiliary mirror that reflects the light emitted from the arc tube into a region to be illuminated toward a reflector. See, for example, Japanese Patent Application Publication No. 11-143378 (FIG. 1) and No. 6-289394 (FIG. 1).
FIG. 7 is a schematic diagram of a related art light source lamp disclosed in JP-A-11-143378. FIG. 8 is a schematic diagram of a related art light source lamp disclosed in JP-A-6-289394.
As shown in FIG. 7, the light source lamp 710 disclosed in JP-A-11-143378 is constructed in such a manner that the light emitted from an arc tube 712 into a region to be illuminated is reflected toward a reflector 714 by an auxiliary mirror 716 mounted to the arc tube 712. As shown in FIG. 8, the light source lamp 810 disclosed in JP-A-6-289394 is constructed in such a manner that the light emitted from an arc tube 812 into a region to be illuminated is reflected toward a reflector 814 by an auxiliary mirror 816 made of a reflection layer formed on the arc tube 812.
Accordingly, the light source lamps 710 and 810 are allowed to make use of the light from the arc tube, which has not been used effectively because it is radiated toward a region to be illuminated, by using the auxiliary mirrors 716 and 816, respectively, to increase light use efficiency. Also, there is no need to use a large-scale reflector that covers the arc tube, allowing the reduction in the size of the light source lamp.
However, with such related art light source lamps including the auxiliary mirror, even when the base material or reflection layer of the auxiliary mirror is made of an infrared transparent material, the maximum temperature of an electrode (an electrode A shown in FIGS. 7 and 8) of a pair of electrodes of the arc tube adjacent to the auxiliary mirror tends to become as high as 30° C. to 50° C. under the present circumstances. This results in the problem that the electrode adjacent to the auxiliary mirror is deteriorated earlier than that without the auxiliary mirror, resulting in a decrease in the life of the arc tube.